Conventional articles of athletic footwear include two primary elements, an upper and a sole structure. The upper provides a covering for the foot that comfortably receives and securely positions the foot with respect to the sole structure. The sole structure is secured to a lower portion of the upper and is generally positioned between the foot and the ground. In addition to attenuating ground reaction forces, the sole structure may provide traction, control foot motions (e.g., by resisting over pronation), and impart stability, for example. Accordingly, the upper and the sole structure operate cooperatively to provide a comfortable structure that is suited for a variety of athletic activities.
The upper forms a void on the interior of the footwear for receiving the foot. The void has the general shape of the foot, and access to the void is provided by an ankle opening. Accordingly, the upper extends over the instep and toe areas of the foot, along the medial and lateral sides of the foot, and around the heel area of the foot. A lacing system is often incorporated into the upper to selectively increase the size of the ankle opening and permit the wearer to modify certain dimensions of the upper, such as girth, to accommodate feet with varying proportions. In addition, the upper may include a tongue that extends under the lacing system to enhance the comfort and adjustability of the footwear, and the upper may include a heel counter to limit significant rearward, lateral, and medial movement of the heel.
The sole structure generally incorporates multiple layers that are conventionally referred to as a sockliner, a midsole, and an outsole. The sockliner is a thin, compressible member located in the void within the upper and adjacent to a plantar (i.e., lower) surface of the foot to enhance footwear comfort. The midsole, which is conventionally secured to the upper along the length of the footwear, forms a middle layer of the sole structure and is primarily responsible for attenuating ground reaction forces. The outsole forms the ground-contacting element of the footwear and is usually fashioned from a durable, wear-resistant material, such as rubber, that includes texturing or cleat elements to improve traction.
As noted above, the void formed by the upper has a shape that is suitable for receiving the foot. Individuals may, however, place additional elements within this void, such as supplemental arch supports, aftermarket sockliners, and orthotic inserts, for example. Given that the void has a shape that is suitable for receiving the foot, placing additional elements within the void displaces a portion of the volume within the void that was originally reserved for the foot. That is, placing one or more of an arch support, aftermarket sockliner, and orthotic insert within the void decreases or otherwise modifies the amount of space available for the foot and the proportions of the space available for the foot. In addition to decreasing the amount of space available for the foot, placing one or more of an arch support, aftermarket sockliner, and orthotic insert within the void has the potential to elevate the foot relative to the ground, which may increase the inversion or eversion moment at the ankle joint during use.